Installation - 3
37
Table 3-3. 4-Pin Connector Configurations
PIN
TRIGGER
FAULT/INHIBIT
DIGITAL I/O
1
Not used
FLT Output
Output 0
2
Not used
FLT Common
Output 1
3
Trigger Input
INH Input
Input/Output 2
4
Trigger Common
INH Common
Common
When functioning in Fault/Inhibit mode, the fault (FLT) output, also referred to as the DFI (discrete fault
indicator) signal, is an open collector circuit that pulls the positive output low with respect to the
negative (chassis-referenced) common. The high impedance inhibit (INH) input, also referred to as the RI
(remote inhibit) signal, is used to shut down the dc source output whenever the INH + is pulled low with
respect to the INH (chassis-referenced) common. Figure 3-9 shows how you can connect the FLT/INH
and trigger input circuits of the dc source.
In example A
, the INH input connects to a switch that shorts the Inhibit pin (+) to common whenever it
is necessary to disable output of the unit. This activates the remote inhibit (RI) circuit, which turns off
the dc output. The front panel Prot annunciator comes on and the RI bit is set in the Questionable Status
Event register. To re-enable the unit, first open the connection between pins INH + and common and then
clear the protection circuit. This can be done either from the front panel or over the GPIB.
In example B
, the FLT output of one unit is connected to the INH input of another unit. A fault
condition in one of the units will disable all of them without intervention either by the controller or
external circuitry. The computer can be notified of the fault via a service request (SRQ) generated by the
Questionable Status summary bit. Note that the FLT output can also be used to drive an external relay
circuit or signal other devices whenever a user-definable fault occurs.
FLT
Output
INH
Input
B) FLT Example with Multiple Units
FLT
Output
INH
Input
Switch
(Normally
Open)
INH Common
INH Input
A) INH Example with One Unit
INH FLT
. . . .
INH FLT
. . . .
NOTE: Connectors
are removable
+ - +
+ - +
4 3 2 1
4 3 2 1
4 3 2 1
C) Measurement trigger example
TRG N.U.
. . . .
+
4 3 2 1
NOTE: Connectors
are removable
Trigger signal
or contact closure
Signal Common
Figure 3-9. FLT/INH Examples
In example C
, when functioning as a measurement trigger input, a negative-going edge signal applied to
the TRG input sends an external trigger signal to the trigger system. You can either apply a negative-
going edge signal to the TRG input pin (referenced to common), or apply a contact switch to short the
TRG input to common. Note that in this configuration, pins 1 and 2 are not used.
